An Extremely Bright Slow-rising Afterglow from an Off-axis Jet in GRB 260310A

Abstract We present a multiwavelength study of GRB 260310A, a nearby long-duration gamma-ray burst (GRB) at z ≃ 0.153 associated with a broad-lined Type Ic supernova. Despite its modest prompt gamma-ray output, E γ ,iso ≃ 3.5 × 10 50 erg, GRB 260310A exhibits one of the brightest afterglows ever observed in the X-ray, optical, and radio bands. Its apparent brightness is not its only remarkable feature. The optical afterglow displays a delayed onset, characterized by a slow rising phase, with slope α ≈ −1, and a late peak at ∼0.1 day. We argue that the combination of weak prompt emission, hard peak energy, and late afterglow onset is naturally explained by a GRB jet viewed off-axis. The radio spectral energy distributions are consistent with synchrotron radiation and indicate the presence of both reverse- shock (RS) and forward-shock (FS) components, thus providing a first test of RS models in an off-axis geometry. The X-ray afterglow displays a prominent rebrightening, monitored for up to ∼68 days with no evidence of spectral evolution. A low level of linear polarization, Π ≈ 1.7%, is measured at 15 GHz at T 0 + 55 days and suggests that, at these late times, the FS is the dominant emission component from radio to X-rays. This late-time rebrightening represents a critical test for the two-component jet model. If interpreted as the emergence of a narrow jet core viewed further off-axis, it would imply extreme luminosities and energetics for an on-axis observer.

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Journal
The Astrophysical Journal Letters
Published
2026-10-28
DOI
https://doi.org/10.3847/2041-8213/aea990
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
0.00

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article

An Extremely Bright Slow-rising Afterglow from an Off-axis Jet in GRB 260310A

Sergiy Guziy, Maria I. Gritsevich, Hendrik van Eerten, Eleonora Troja et al.
2 links
The Astrophysical Journal Letters
Gamma-ray bursts and supernovae
article

An Extremely Bright Slow-rising Afterglow from an Off-axis Jet in GRB 260310A

Sergiy Guziy, Maria I. Gritsevich, Hendrik van Eerten, Eleonora Troja, Alžběta Maleňàkovà, A. Sota, Martin Jelínek, Daniel Gruen, D. Hiriart, Jorma Ryske, Jesús Aceituno, Narjes Shahamat, Yu-Han Yang, Brendan O’Connor, Y. D. Hu, Simone Dichiara, J. Štrobl, Rubén Sánchez-Ramírez, Ignacio Pérez-García, M. D. Caballero‐García, Shashi B. Pandey, Emilio Fernández-García, Alberto J. Castro-Tirado, Malte Busmann, Muskan Yadav, Hira Waseem, Niccolò Passaleva, Ivan Agudo, Alexander Kutyrev, Filip Novotný, Siyu Wu, Yi-Han Iris Yin, V. Galluzzi, Roberto Ricci
article en

Abstract

Abstract We present a multiwavelength study of GRB 260310A, a nearby long-duration gamma-ray burst (GRB) at z ≃ 0.153 associated with a broad-lined Type Ic supernova. Despite its modest prompt gamma-ray output, E γ ,iso ≃ 3.5 × 10 50 erg, GRB 260310A exhibits one of the brightest afterglows ever observed in the X-ray, optical, and radio bands. Its apparent brightness is not its only remarkable feature. The optical afterglow displays a delayed onset, characterized by a slow rising phase, with slope α ≈ −1, and a late peak at ∼0.1 day. We argue that the combination of weak prompt emission, hard peak energy, and late afterglow onset is naturally explained by a GRB jet viewed off-axis. The radio spectral energy distributions are consistent with synchrotron radiation and indicate the presence of both reverse- shock (RS) and forward-shock (FS) components, thus providing a first test of RS models in an off-axis geometry. The X-ray afterglow displays a prominent rebrightening, monitored for up to ∼68 days with no evidence of spectral evolution. A low level of linear polarization, Π ≈ 1.7%, is measured at 15 GHz at T 0 + 55 days and suggests that, at these late times, the FS is the dominant emission component from radio to X-rays. This late-time rebrightening represents a critical test for the two-component jet model. If interpreted as the emergence of a narrow jet core viewed further off-axis, it would imply extreme luminosities and energetics for an on-axis observer.

The Astrophysical Journal LettersVol. 1011(1)
Petro Mohyla Black Sea National University (UA), University of Rome Tor Vergata (IT), Pennsylvania State University (US), Consejo Superior de Investigaciones Científicas (ES), Guangxi University (CN), Czech Academy of Sciences (CZ), Masaryk University (CZ), Trieste Astronomical Observatory (IT), Aryabhatta Research Institute of Observational Sciences (IN), Excellence Cluster Origins (DE), Istituto di Radioastronomia di Bologna (IT), National Aeronautics and Space Administration (US), Ursa Astronomical Association (FI), Instituto de Astrofísica de Andalucía (ES), University of Bath (GB), University of Maryland, College Park (US), Carnegie Mellon University (US), Ludwig-Maximilians-Universität München (DE), Universidad de Málaga (ES), Sapienza University of Rome (IT), National Institute for Astrophysics (IT), University of Hong Kong (HK), Universidad Nacional Autónoma de México (MX)
European Space Agency, Chinese Academy of Sciences, Junta de Andalucía, Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas
Openalex Percentile: Top 62%
Gamma-ray bursts and supernovae
DOIOpen Access PDFOpenAlex
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